Add piMemorySize for rpi4

#include <stdio.h>

int main()
{
	int bRev, bType, bProc, bMfg, bMem, bWarranty ;
	int revision = 12595474; //Convert hexadecimal to decimal
	bRev      = (revision & (0x0F <<  0)) >>  0 ;
        bType     = (revision & (0xFF <<  4)) >>  4 ;
        bProc     = (revision & (0x0F << 12)) >> 12 ;	// Not used for now.
        bMfg      = (revision & (0x0F << 16)) >> 16 ;
        bMem      = (revision & (0x07 << 20)) >> 20 ;
       bWarranty = (revision & (0x03 << 24)) != 0 ;
       printf ("piBoardId: rev: %d, type: %d, proc: %d, mfg: %d, mem: %d, warranty: %d\n",
		bRev, bType, bProc, bMfg, bMem, bWarranty) ;

   return 0;
}

/* revision see https://www.raspberrypi.org/documentation/hardware/raspberrypi/revision-codes/README.md 
*RPI revision is HEX.*\

wiringPi/wiringPi.c

@@ -288,8 +288,8 @@ const int piMemorySize [8] =
    256,		//	 0
    512,		//	 1
   1024,		//	 2
-     0,		//	 3
-     0,		//	 4
+  2048,		//	 3
+  4096,		//	 4
      0,		//	 5
      0,		//	 6
      0,		//	 7